Phase change of volatile liquids across small temperature gradients is used in the Organic Rankine Cycle to generate electricity in geothermal and other applications. Use of a relative high temperature body versus a relative low temperature body enables transfer of thermal energy from the relative high temperature body to the relative low temperature body by action of a circulating fluid. Phase change of the fluid from liquid to gaseous phase at the relative high temperature body results in adiabatic expansion, whereby work is performable by the fluid before re-condensation at the relative low temperature body. Cycling of the fluid across this thermal differential therefore enables repeated phase change and further work performable by the fluid to generate electricity.
The present invention makes use of a volatile working fluid having a low boiling point. The working fluid is forcible through a fluid circuit internal to an impermeable housing wherein phase change is effective at temperatures typical in the natural world. By partial submergence in a water body, the device is adapted to maintain a fluid circuit between each of a first heat exchanger, maintained above the air-water interface, and a second heat exchanger, submerged at a depth within the water body. The temperature differential extant between the water body and the ambient atmosphere above the air-water interface thus enables continual transfer of thermal energy usable to drive a heat engine integral with the device. Due to diurnal, nocturnal, and seasonal temperature cycles, wherein the temperature of the water body is alternately colder and warmer than the atmosphere, a plurality of sensors is included to control and reverse the direction of the fluid circuit, and optimize production of electricity from mechanical action driven at the heat engine.